To begin with a further introduction, a quotation from Technology Notes, published by WaterAid, a registered UK charity, 47-49 Durham St., London, England SE11 5JD (referred to as WaterAid Technology notes) gives a good background:                “Wherever possible, a water source that is chosen for development should be one which does not require treatment in order to give a satisfactory quality of water. A source which is relatively expensive to develop can often be more economical in the long-run than a source which is cheaper to develop but which requires daily maintenance—or even if it requires maintenance only weekly.        A community water supply scheme must be within the capacity, both financial and technical, of the benefiting community to operate and maintain it. It is more likely to be sustainable if the emphasis of the project is on the protection of the sources of water so as to maintain safe water quality rather than on the treatment of polluted water. Sometimes it is necessary to develop a source for purposes other than drinking, such as bathing or clothes washing, where a reasonable supply quality is needed to combat “water washed” diseases.        Ground water from wells or springs is usually of an acceptable quality, due to natural filtration through the ground. However, water from surface sources such as streams, lakes and ponds will usually require some form of treatment. The quality of this water may vary greatly with the seasons of the year. The treatment of surface water can be an expensive exercise and one which it is difficult for communities to sustain without long-term external support. Routine maintenance is essential and, in addition, an ability to vary the method of treatment so as to respond to changes in water quality is required. The ultimate water treatment, namely, using chemicals, is not considered viable in sustainable community development.        Three simple methods of treatment are considered viable: settlement, roughing filtration and slow sand filtration. Either of the first two will improve the appearance of the water but the third, particularly when used with one of the first two, should give a clear and bacteriologically pure water.”Water Aid Technology Notes at p. 44.        
The purpose of this invention is to attempt to utilize more modern no-maintenance technology to achieve cleaner water.
As initially stated, and as WaterAid emphasizes, it is always easier to clean already mostly or completely clean water, but the realities of the 3rd and 4th world are that surface water is a common and the only viable source for the truly impoverished because it is free. So, the objective has to be to improve the only source and reduced disease and problems from water borne contamination.
Another harsh reality is that absent a complex and large organization, it is very difficult to find money or even ship the parts to accomplish a sustainable water-cleansing system. Theft, and the necessity for non-hand-carried luggage to be guarded and secured is a persistent problem in third world countries. Thus, this design can be dissembled and carried in one or two suitcases. Once built, no one is likely to steal the box of sand which is the filter, but security for the solar panel, battery and converter, even in this simple system, is an issue which a local community would have to address. The UV treatment stage is otherwise useless to a thief absent the integrated system, so it too is less of a theft problem.
As to maintenance, most of the WaterAid systems need some maintenance, perhaps every day or two by someone with some understanding or skill. There are many communities where that is just not realistic.
For example, posit the following observation from WaterAid's Technology Notes:                “The cost of operating the project when it is finished must be considered at an early stage. This may be little more than the cost of payment for the occasional services of a caretaker to clean the apron and steps at a protected spring, handpump or borehole. However, it might be considerably more, such as the cost of maintenance, and possible replacement of parts, for a handpump, or the operation of a diesel driven pump, including the provision of fuel or even the provision and dosing of chemicals for water treatment.        The following list of headings to be considered was used in the preparation of a maintenance budget for self sufficiency for a gravity scheme, from a spring source, supplying 50,000 people in rural Ethiopia.        Salaries                    Office staff            Caretakers                        Maintenance cost                    Labour costs            Materials for repairs                        Office costs                    Maintenance—structure and equipment            Stationery and printing                        Transport cost                    Truck hire to carry out repairs            Caretakers attending the office                        Protective clothing        Hand tools        Meter replacements        Consultants—(to advise on management and engineering)        Training        Motor bikes                    Replacement costs            Running cost                        Two other items to consider (not applicable in this particular example project) are diesel and electricity.”        Water Aid Technology Notes at p. 5.        
While of course the needs are great, and a system for 50,000 people is commendable, much of the world lives in poor subsistence communities that have no possibility of any of the above. The only items these communities have some access to is sunlight and surface water. There is no money for “cost of operating.” More likely is that a partner of an international aid organization will have an employee who circulates from site to site to check them out, identify needs, perform testing if needed, and make a major repair, which in the case of this system, is basically a modular re-insert.
This invention proposes a sustainable solar powered water-cleansing system that is not necessarily perfect, but can be carried in a suitcase on a plane and will considerably improve and perhaps purify water. The objective was to build a system for $500 of materials purchased commercially in U.S. internet and local hardware distribution stores. That objective is likely not attainable at current 2009 prices absent shipping discounts; however, $600 seems doable for raw materials, without the battery, lumber, or labor involved. The concept is that the labor would be obtained overseas. Shipping batteries overseas, especially the cheapest and most practical battery, a lead acid battery, is not realistic, but lead acid car batteries are fairly ubiquitous and can be obtained in every country in the world, and even in fairly remote locations. There are batteries available in which the battery is dry, and the electrolyte is unmixed. The electrolyte can be mixed with clean water and then put in the battery. A hygrometer is needed to initially calibrate the battery. Dirt, sand and gravel for filtering would be procured near the community site where the water cleansing device is erected.